Respiratory changes during continuous epidural blockade

[Nonanalgesic effects of thoracic epidural anesthesia]

Thoracic epidural anesthesia, which has been performed since the 1950s, has progressed from being one analgesic technique among others to its present status as the technique of choice for managing pain after major abdominal and thoracic surgery. In addition to providing effective analgesia, the epidural infusion of local anesthetic agents produces a sympathetic block that offers advantages over other types of pain control, particularly with respect to the cardiovascular, respiratory, and gastrointestinal systems. Thoracic epidural anesthesia provides dynamic pain relief, allowing the patient to resume activity early. It also permits early extubation and is associated with fewer postoperative pulmonary complications, shorter duration of paralytic ileus, and a better response to the stress of anesthesia and surgery. However, meta-analyses have not yet demonstrated that postoperative outcomes are improved. This review describes the nonanalgesic effects of thoracic epidural anesthesia.

Effect of obesity and thoracic epidural analgesia on perioperative spirometry

BACKGROUND

Lung volumes in obese patients are reduced significantly in the postoperative period. As the effect of different analgesic regimes on perioperative spirometric tests in obese patients has not yet been studied, we investigated the effect of thoracic epidural analgesia and conventional opioid-based analgesia on perioperative lung volumes measured by spirometry.

METHODS

Eighty-four patients having midline laparotomy for gynaecological procedures successfully completed the study. Premedication, anaesthesia and analgesia were standardized. The patients were given a free choice between epidural analgesia (EDA) (n=42) or opioids (n=42) for postoperative analgesia. We performed spirometry to measure vital capacity (VC), forced vital capacity, peak expiratory flow, mid-expiratory flow and forced expiratory volume in 1 s at preoperative assessment, 30-60 min after premedication and 20 min, 1 h, 3 h and 6 h after extubation.

RESULTS

Baseline values were all within the normal range. All perioperative spirometric values decreased significantly with increasing body mass index (BMI). The greatest reduction in VC occurred directly after extubation, but was less in the EDA group than in the opioid group: mean of -23(sd 8)% versus -30(12)% (P<0.001). In obese patients (BMI>30) the difference in VC was significantly more pronounced than in patients of normal weight (BMI<25): -45(10)% versus -33(4)% (P<0.001). Recovery of spirometric values was significantly quicker in patients receiving EDA, particularly in obese patients.

CONCLUSION

We conclude that EDA should be considered in obese patients undergoing midline laparotomy to improve postoperative spirometry.

Epidural anesthesia for cesarean section in a patient with Eisenmenger's syndrome

Eisenmenger's syndrome is a complex combination of cardiovascular abnormalities and is defined as pulmonary hypertension at systemic pressure level with reversed or bi-directional shunt through an intracardiac or aortopulmonary communication. Patients with Eisenmenger's syndrome are at high risk for peripartum morbidity and mortality. Multigravid patients with this disease are therefore uncommon. We report the anesthetic management for cesarean section of a 27-year-old multigravid female at 35 weeks' gestation with Eisenmenger's syndrome. Titrated epidural anesthesia was administered with incremental doses of 2% lidocaine. Intraoperative course was uneventful except for an episode of hypotension immediately after delivery of the baby, which was managed successfully. We conclude that carefully titrated epidural anesthesia may be safe, appropriate, and effective for patients with Eisenmenger's syndrome for cesarean section.

Lung aeration and pulmonary gas exchange during lumbar epidural anaesthesia and in the lithotomy position in elderly patients

We investigated a total of 36 subjects with a mean (SD) age of 65 (13) years, during baseline conditions (supine, before any anaesthesia), and then during one of the following protocols: (1) lithotomy positioning (n = 12), (2) epidural anaesthesia (n = 12), (3) general anaesthesia in the supine position (n = 12). Lung aeration, ventilation/perfusion matching, gas exchange and functional residual capacity were measured. Lung aeration was normal during baseline assessment with almost no regions with poor aeration and no substantial dependent densities. Shunt and perfusion of poorly ventilated regions were minor. Lithotomy positioning did not reduce functional residual capacity and did not affect aeration of the lung or ventilation/perfusion matching. Epidural anaesthesia, in general, had no effect on aeration, ventilation/perfusion matching or gas exchange, regardless of whether the patient was in the supine or lithotomy position. General anaesthesia, however, caused significant increases in poorly aerated lung regions and in dependent densities (interpreted as atelectasis). In conclusion, no or little impairment of lung aeration and ventilation/perfusion matching was caused by the lithotomy position and/or epidural anaesthesia, contrary to the effects seen during general anaesthesia. However, our findings also suggest that being overweight is a factor that may cause impairment of lung aeration.

Regional anaesthesia and cough effectiveness. A study in patients undergoing caesarean section

We report the results of a study of the effects of spinal and epidural anaesthesia for Caesarean section on commonly used indicators of a patient's ability to cough effectively. Both spinal and epidural anaesthesia, after the achievement of a block adequate for surgery, were associated with statistically significant decreases (p less than 0.05) in all the respiratory variables recorded: forced vital capacity, forced expiratory volume in one second, peak expiratory flow rate and maximum expiratory pressure. We conclude that although the observed changes are unlikely to impair the normal patient's ability to cough effectively in these circumstances, there may be clinically significant impairment in the presence of an inadvertently high block or in a patient with pre-existing pulmonary disease.

Comparison between propofol and midazolam as sedative agents for surgery under regional anaesthesia

Propofol (25 patients) or midazolam (25 patients) was used to provide sedation in patients who underwent abdominal or orthopaedic surgery under epidural anaesthesia after intravenous premedication with droperidol 1 mg and fentanyl 20 micrograms. The quality of sedation whilst the block was performed, was assessed as good in 19 patients after propofol 1.49 mg/kg but six patients exhibited uncontrolled movement. Good sedation was provided in 22 patients after midazolam 3 mg. A mean infusion rate of propofol of 1.74 mg/kg/hour resulted in easily controllable sedation during the procedure. Eleven patients given midazolam required no further sedation but a mean of 5.79 mg was needed in the remaining 14 patients; the dose was unpredictable in individual patients. Recovery was significantly more rapid in the propofol group.

Respiratory effects of high thoracic epidural anaesthesia

The respiratory effects of high thoracic epidural anaesthesia (TEA) were studied in nine healthy volunteers by means of spirometry, nitrogen single-breath test and flow-volume loop. After the baseline measurements an epidural catheter was inserted at T4 level, and 5 ml of 0.5% bupivacaine were injected. This volume led to sensory block within dermatomes T1-T5. Total lung capacity, vital capacity and inspiratory capacity decreased slightly but significantly during TEA. Expiratory reserve volume was not affected. Maximal inspiratory flow at 50% VC decreased 24%. Maximal expiratory flow at 75% VC and peak expiratory flow were not changed. N2 difference during a constant flow rate of 0.5 l/s and forced expiratory volume in 1 s were not changed, which indicates that there were no changes of bronchial tone. The respiratory effects of high TEA in this study were caused by the motor block of the intercostal muscles.

Respiratory performance after upper abdominal surgery. A comparison of pain relief with intercostal blocks and centrally acting analgesics

The respiratory capacity was studied during the first 2 days postoperatively in 94 patients, aged 19 to 75 years and undergoing surgery through an upper abdominal incision. Postoperative pain relief was randomly administered, either by intercostal block (i.c.b.) and centrally acting analgesics on demand, or by centrally acting analgesics alone. Respiratory studies comprising forced vital capacity (FVC), forced expiratory volume in one second (FEV1), peak expiratory flow rate (PEF) and analysis of arterial blood gases were made. Bilateral i.c.b. given after surgery performed through a midline incision did not improve the respiratory function, whereas unilateral i.c.b. after surgery through a subcostal incision had positive effects. Thus postoperative i.c.b. following cholecystectomy performed through a subcostal incision resulted in higher FVC, FEV1 and PEF values than without i.c.b. at least during the time of effective nerve block. I.c.b. after subcostal incision also improved arterial oxygen tension. The patients undergoing cholecystectomy and receiving a second i.c.b. 8 h after the first one had better respiratory function than the patients without any block during the first 2 days postoperatively.

Ventilation-perfusion relationships during epidural analgesia

Resting lung volume (FRC), airway closure (CC) and ventilation-perfusion relationships, using the multiple inert gas elimination technique, were studied during epidural analgesia. The material consisted of 10 patients, 55-84 years of age. Epidural blockade (9-13 ml mepivacaine-adr, 1/200,000) was instituted to an upper level corresponding to Th3-Th6. Minute ventilation and breathing frequency remained unchanged during the epidural block, while cardiac output was significantly increased (4.80-5.74 l/min). The relationship between FRC and CC (FRC-CC) was unchanged during the block, indicating an unchanged magnitude of airway closure. Multiple inert gas elimination data revealed virtually unchanged distribution of ventilation and perfusion during the epidural block in 9 of the 10 patients. It is concluded that lumbar epidural analgesia up to Th3-Th6 does not influence the degree of airway closure, nor does it cause VA/Q mismatching as general anaesthesia does.

Central blood pooling as an explanation for lowered FRC during anaesthesia? Thigh volume measurements by plethysmography

Segmental volumes of the thigh and the upper arm were measured by means of an air-filled plethysmograph before and during various anaesthesias. A small but significant fall in segmental volume was seen with the induction of anaesthesia with thiopentone. A further fall was observed during neurolept anaesthesia but not with halothane. Epidural and spinal anaesthesias caused no change in segmental thigh volume. The results suggest a redistribution of 50-150 ml blood from the extremities to the trunk during general anaesthesia. This redistribution may contribute to the well-known fall in FRC with general anaesthesia.

Postoperative analgesia

Postoperative analgesia both by drugs and regional techniques is reviewed. In the United Kingdom in the last 25 years or more there has been little advance on either front. Some marginal improvement in regard to drugs might be brought about by better education of both doctors and nurses and better patient contact. Extradural analgesia and intercostal block do not offer a complete solution, though a judicious increase in the use certainly of the former might be beneficial. The problem awaits a radical new approach.

Effects of intercostal nerve blocks (bupivacaine 0.25% and etidocaine 0.5%) on chest wall mechanics in healthy men

Bilateral blockade of the 5th to 11th intercostal nerves, inclusive, was produced in 14 healthy subjects. In seven, bupivacaine 0.25% was used, and in the other seven, etidocaine 0.5%. The latter has been found to have a stronger motor-blocking action than the former. Before and after the blockade, the vital capacity (VC), peak expiratory flow rate (PEF), tidal volumes, respiratory variations in rib cage and abdominal circumferences and in oesophageal and intragastric pressures were recorded. By transthoracic electrical impedance pneumography, measures indicating changes in the functional residual capacity (FRC) were obtained. Although it was considered that changes in the parameters investigated mainly demonstrated changes in motor function, no differences were found between the drugs. With this form of blockade they seem to have equivalent effects in this respect. Thus, VC decreased by an average of 7% and PEF by 6%. Signs of a reduction of FRC after the blockade were also observed. The blockade had no effect on the partitioning of costal and abdominal breathing at rest. Analysis of the relations between the fractions of costal and abdominal breathing and the corresponding variations in intragastric pressure gave support to the view that in normal individuals both intercostal and abdominal muscles remain passive during respiration at rest. This is thus achieved by the diaphragm alone.

Thoracic epidural analgesia-II: prolongation in the early postoperative period by continuous injection of 1.0% bupivacaine

Sixteen patients were given thoracic epidural analgesia at the T5-T6 level with 2 ml of 1.0% bupivacaine solution plain for pain relief after upper abdominal surgery. In 13 cases the analgesia was prolonged by continuous injection of 1.0% bupivacaine for 24 or 48 h. Onset time and segmental spread of the analgesia are presented as well as segmental spread, intensity of the blockade, and peak expiratory flow rates during prolongation. Signs of tachyphylaxis were noticed, and also signs of accumulation of bupivacaine in plasma. A high incidence of urinary retention occurred. The method is not considered to be ideal for pain relief after upper abdominal surgery.

Thoracic epidural analgesia I-a double-blind study between bupivacaine and etidocaine

A double-blind comparison was made in 40 patients undergoing thoracic epidural analgesia with either bupivacaine 0.5% or etidocaine 1.0%, both with adrenaline 5 mug/ml. All patients were undergoing elective upper abdominal surgery. They were studied both pre- and postoperatively. The parameters measured were: onset time, segmental spread and duration of analgesia; and also systolic blood pressure, heart rate and peak expiratory flow rate. In respect of these parameters, no major differences were found between the two solutions under the conditions of the study. The overall results, however, differ in many respects to those found when these agents are used in lumbar epidural analgesia.